1. Field of the Invention
The present invention relates to a liquid discharge method, droplet discharging apparatus, and inkjet recording apparatus, and more specifically to a liquid filling method that effectively eliminates bubbles inside a pressure chamber in communication with a nozzle (droplet discharging port), to a droplet discharging apparatus, and to an inkjet recording apparatus that uses the discharge apparatus.
2. Description of the Related Art
In an inkjet recording head, pressure is applied to liquid inside a pressure chamber to discharge droplets of the liquid through a nozzle connected to the pressure chamber. If bubbles are present in the pressure chamber, there is a drawback in that no droplet is discharged because energy is expended on shrinking the bubbles when the pressure is applied to the liquid. Bubbles are easily formed in the pressure chamber when the liquid is filled thereinto. For this reason, the pressure chamber must be designed so that no bubble remains therein.
As methods that do not leave bubbles inside the head, or that effectively remove bubbles inside the head, several methods have been proposed whereby the interior of the pressure chamber is subjected to hydrophilization treatment (Japanese Patent Application Publication Nos. 5-124198, 5-318725, 6-71885, and 8-108535).
The inkjet recording head disclosed in Japanese Patent Application Publication No. 5-124198 features a crater portion formed in the nozzle plate, and the crater portion, the inside walls of the head, and ink flow channels are subjected to hydrophilization treatment. Cited therein is the preference that the hydrophilization treatment be carried out so that a contact angle of purified water at normal temperature on the treated surface is 10° or less. However, this configuration requires a nozzle plate with a complicated structure, and considerable labor is required in its fabrication.
In the inkjet recording head disclosed in Japanese Patent Application- Publication No. 5-318725, the cover plate with flow channels has a two-layer structure, the contact angle of the ink on the layer on the side in contact with the ink is 90° or less, and the contact angle of the ink on the layer on the side not in contact with the ink is 90° or greater. However, this configuration has a complex structure because the cover plate has the two layers.
The inkjet recording head disclosed in Japanese Patent Application Publication No. 6-71885 is configured so that at least a portion of the ink-contacting area inside the head is subjected to hydrophilization treatment with an ion injection method. Also disclosed in this publication is an aspect in which an orifice plate (equivalent to a nozzle plate) is formed with a water-repellent material, and the reverse surface of the discharge port formation surface is subjected to the hydrophilization treatment. However, this configuration uses the ion injection method, so that the hydrophilization treatment step is rather labor intensive.
The inkjet recording head disclosed in Japanese Patent Application Publication No. 8-108535 is a plastic head, and the contact angle of the ink on the inner surface of the ink flow channels is 10° or less. However, this configuration is limited to a plastic head, and cannot be applied to heads manufactured using materials (stainless steel or the like, for example) other than plastic.